1. Field of the Invention
The present invention relates generally to a lighting system for use with a vehicle and more specifically to an apparatus used to collect and transmit light.
2. Description of the Related Art
Conventional vehicle lighting systems typically utilize a bulb and reflector combination. In a bulb and reflector combination, a filament of the bulb is placed at or near a focal point of the reflector. The focal point of a reflector is that point at which parallel rays of light meet after being reflected by the reflector. Conversely light rays emanating from the focal point are reflected as parallel rays of light. Energy supplied to the filament radiates as light over a 4.pi. steradian solid angle. A portion of the radiated light is collected by the reflector and reflected outward. The outwardly reflected light is passed through a lens to form a light beam.
With the advent of light guides such as fiber optics, the ability to use a remote light source and a fiber optic light guide to transfer light generated at the remote light source to a distant location became available. A system of reflectors and lenses is typically used to direct light emitted from the light source, such as a bulb filament, into the end of a fiber optic light guide. The amount of light that can be effectively directed into the fiber optic light guide varies with respect to the numerical aperture of the fiber optic light guide. The numerical aperture is a number which corresponds to the acceptance angle; i.e. the critical angle at which light striking the end of the fiber optic light guide will enter the light guide. Light striking the light guide at an angle greater than the critical angle will reflect off the face of the fiber optic light guide and become unusable light thus lowering the collection efficiency.
Until recently, the importance of the critical angle with respect to the end of the fiber optic light guide was not recognized and the fiber optic light guide was simply brought closer to the light source. However, this resulted in a greater amount of light striking the end of the fiber optic light guide at an angle greater than the critical angle resulting in a decreased collector efficiency. In an attempt to increase the amount of light entering the fiber optic light guide, reflective and focusing systems were developed.
An example of such a system is disclosed in U.S. Pat. Nos. 4,241,382 and 4,755,918. These patents disclose reflective systems having a combination of elliptical and spherical mirrors to direct and focus the light emitted from a bulb filament onto the end of a fiber optic light guide. The light emitted from the source is reflected by a spherical reflector and returned through the source prior to striking an elliptical reflector which focuses the light onto the end of the fiber optic light guide.
Since losses occur at each reflective surface, each additional reflection reduces the efficiency of the apparatus. Also, when the light is reflected through the filament, additional losses occur due to the light ray striking the filament. The filament is not a point source, thus each reflection of the light increases the deviation from the desired path of travel until the deviation becomes significant and the reflected light ray is no longer focused upon the fiber optic light guide. Finally, these systems tend to focus all of the light onto the small area of the elliptical reflector. Since the light source or bulb filament is not a point source the system becomes very sensitive to filament size and location, resulting in greater angular deviation of the light ray.
Typically a greater intensity light source is used to make up for any inefficiencies of a reflective system. However, even with a relatively efficient light source each watt of power supplied to the bulb filament results in only 0.25 watts of optical energy (light), and the remaining 0.75 watts is non-optical energy (heat). Thus the use of a higher intensity light source results in excessive heat.
Therefore, it is desireable to have a highly efficient compact apparatus which collects and focuses light produced by a bulb filament in a predetermined pattern onto the end of a fiber optic light guide and at angle less than the critical angle of the fiber optic light guide. It is further desired to avoid reflected and redirected light from passing back through the filament. The occurrences of reflection of the light rays should be kept to a minimum prior to entering the fiber optic light guide to reduce any additional losses due to reflection and defocusing of the light rays.